This invention pertains to an aqueous inkjet ink, in particular to an aqueous inkjet ink comprising an aqueous vehicle, a colorant and a bleed control agent.
Inkjet printing is a non-impact printing process in which droplets of ink are deposited on a substrate, such as paper, to form the desired image. Inkjet printers are equipped with an ink set which, for full color printing, typically comprises a cyan, magenta and yellow ink (CMY).
Bleed of one color into another is a typical problem in ink jet printing because inks have relatively low viscosity and tend to spread especially for inkjet printers having capability of printing three or four primary colors in a simultaneous (or near simultaneous) fashion. Such bleed of one printing liquid into an adjacent printing liquid results in production of indistinct images with a poor degree of resolution.
Various methods have been proposed to prevent bleed of adjacent printing liquids. One method is to apply the two printing liquids at a distance from one another so that no intermingling or mixing of the printing liquids can occur. However, this method produces images of poor resolution. Another method involves a delay in applying the second printing liquid until the first printing liquid is completely dry. This method is disadvantageous due to its inefficiencies. Yet another approach to control bleed is to increase the rate of penetration of the printing liquid into the substrate, but this causes a reduction of optical density.
U.S. Pat. No. 6,280,513 discloses an ink comprising a self-dispersing pigment and certain salts to improve optical density and bleed properties. The ink may further comprise an antioxidant including catechol. However, it does not describe the combination of a self-dispersing pigment and catechol.
While the use of inorganic or organic salts in one or more inks of the ink set has provided improved bleed property in inkjet printing, a need still exists for improved inkjet ink formulations that provide good print quality without the drawbacks of having high concentration of salts in inks. The present invention satisfies this need by providing compositions having improved optical density and bleed property.